Starter device for single phase ac motors

ABSTRACT

A starter device for a single phase A.C. motor having a main winding and a starting winding adapted for connection to a single phase A.C. source. The starter device includes a semi-conductor switching device having a control electrode and a transconductive path, and a transformer having a first and a second primary windings arranged to generate opposite fluxes in the transformer core, and a secondary winding. The starter device includes a circuit for connecting the first primary winding in series with the main winding of the motor and another circuit for connecting the second primary winding in series with the transconductive path of the switching device and with the starting winding of the motor. The control electrode of the switching device is connected to the secondary winding of the transformer whereby the voltage induced in the secondary winding by the initial inrush of current flowing through the first primary winding upon starting of the motor will render the switching device conductive to permit energization of the starting winding of the motor to start the same. The flux produced by the second primary winding shortly after initiation of conduction in the switching device will oppose the flux created by the first primary winding and so reduce the voltage induced in the secondary winding to stop conduction through the switching device and thus disconnect the starting winding of the motor.

United States Patent- Ramirez 1 May 30, 1972' Antonio Ramirez, 5885 ParkAvenue, Montreal, 152 Quebec, Canada 221 Filed: Apr.26, 1971 211Appl.No.: 137,199

[72] Inventor:

[57] ABSTRACT A starter device for a single phase A.C. motor having amain winding and a starting winding adapted for connection to a singlephase A.C. source. The starter device includes a semiconductor switchingdevice having a control electrode and a transconductive path, and atransformer having a first and a second primary windings arranged togenerate opposite fluxes in the transformer core, and a secondarywinding. The starter device includes a circuit for connecting the firstprimary winding in series with the main winding of the motor and another{30] Foreign Application Priority Dag circuit for connecting the secondprimary winding in series Jan. 13, 1971 Canada 102099 with the tranconductive path of the switching device and with the starting winding ofthe motor. The control electrode of the [52] U.S. Cl ..3l8/221 E,318/227 switching d i i ted to the secondary winding of the [5 l IIIILCl. i ..H02 1/44 transformer whereby the voltage induced in he Secondary[58] Field of Search ..3l8/220 R, 221 R, 221E, 227 winding by theinitial imush of current flowing through the first primary winding uponstarting of the motor will render the switching device conductive topermit energization of the [56] References cued starting winding of themotor to start the same. The flux UNITED STATES PATENTS produced by thesecond primary winding shortly after initiatron of conduction in theswitching device will oppose the flux 3,376,484 4/1968 Lewus ..3l8/22l Ecreated b the first primary winding and so reduce the voltage 3,573,5794/1971 Lewus ..318/221 E I induced in the Secondary winding to Stopconduction through D the switching device and thus disconnect thestarting winding Primary Examiner-Gene Z. Rubmson of the momAttorney-Raymond A. Robic 4 Clains, 2 Drawing Figures L1 L2 0 b 0 M i rTRI Patent ed May 30, 1912 3,667,017

FIG-5.2

Anton/'0 RAM/RFZ r M AffdF/V') STARTER DEVICE FOR SINGLE PHASE AC MOTORSThe invention relates to a starter device for a single phase A.C motor.

Conventional single phase A.C. motors normally include two statorwindings, a running winding which operates the motor and a startingwinding which is used to start the motor. The starting winding is neededbecause the running winding does not provide any torque until the rotorof the motor rotates. It is therefore known practice to energize bothwindings until the desired speed is reached and then to disconnect thestarting winding.

The starter devices of the prior art included centrifugal switches orrelays which were subject to arcing and wear of moving parts. Suchelectromechanical devices were bulky and, furthermore, could not be usedin locations where explosions could occur because of arcing problems. Inaddition,

they had to be adjusted for each motor they were used with.

Recently, the electromechanical devices have been replaced bysemi-conductor switches. Commonly, one or more semi-conductor switchesare connected in series with the starting winding of the motor and areopened or closed depending upon a control voltage derived from a currentsensing device serially connected with the main winding and responsiveto the decrease of the current in the running winding of the motor asspeed increases. Such devices are much more compact than theelectromechanical devices and are not subject to arcing and wear sincethey do not have moving parts. They may also be encapsulated andthus'protected against vibrations, dust, humidity, etc.

However, it has been found that the current sensing devices of theabove-mentioned semi-conductor switching devices could not be used withall sizes of motors. In fact, in the more common range of 1/6 to 1 HPmotors, it was found that a great number of sensing devices wererequired because of the variations in the current to be sensed.

It is therefore the main object of the invention to provide a starterdevice for AC. motors which may be utilized with a wide range of motorshaving different horsepower ratings and yet provide all the advantagesof the semi-conductor switching devices.

The starter device, in accordance with the invention, includes asemi-conductor switching device having a control electrode and atransconductive path, anda transfonner hav ing a first and a secondprimary windings arranged to generate opposite fluxes in the transformercore, and a secondary winding. The starter device includes a circuit forconnecting the first primary winding in series with the main winding ofthe motor and a second circuit for connecting the second primary windingin series with the transconductive path of the switching device and withthe starting winding of the motor. The control electrode of theswitching device is connected to the secondary winding of thetransformer, whereby the voltage induced in the secondary winding by theinitial inrush of current through the first primary winding uponstarting of the motor will render the switching device conductive topermit energization of the starting winding of the motor to start thesame. The flux produced by the second primary winding, shortly afterinitiation of the conduction of the switching device, will oppose theflux created by the first primary winding and reduce the voltage inducedin the secondary winding to stop conduction through the switching deviceand thus disconnect the starting winding of the motor.

In addition, a thermistor is connected across the secondary winding forabsorbing the voltage surges induced in the secondary winding of thetransformer due to sudden overloads of the motor during operationcausing corresponding increases of the current through the first primarywinding.

In a second embodiment of the invention, the thermistor is replaced by apotentiometer which also permit to adjust at will the potential to beapplied to the control electrode of the switching device thus extendingthe use of the starter device to a wider range of motor voltages, speedsand powers.

companying drawings in which:

FIG. 1 illustrates a first embodiment of the invention; and

FIG. 2 illustrates a second embodiment of the invention.

Referring to FIG. 1, there is shown a starter device in accordance withthe invention and including a transfonner T having two primary windingsP1 and P2 wound in opposite direction on the transformer core, and asecondary winding S. The first primary winding P1 is connected in serieswith the running winding RU of the motor M across tenninals L1 and L2 ofa suitable A.C. source through conventional manual switch SW. The secondprimary winding P2 of the motor is connected to terminals L1 and L2through the transconductive path of a semi-conductor switching deviceTRI which may advantageously be of the TRIAC type, in series with thestart ing winding ST and the phasing capacitor C of the motor.

The secondary winding S of the transformer has one terminal connected tothe control electrode of the semi-conductors switching device TRI andthe other to the common terminal L l of the source. A thermistor TH isconnected across secondary winding S of the transformer.

The operation of the starter device in accordance with the invention isas follows:

Upon closure of switch SW, current starts to flow through the primarywinding P1 of transformer T and through the running winding RU of themotor. The initial inrush of current through the running winding of themotor will induce a voltage in secondary winding S of the transformer Tand such voltage will be applied to the control, electrode ofsemi-conductor switching device TRI to render the switching deviceconductive.

The conduction of switching device TRI will cause current to flowthrough the second primary winding P2 of transformer T and through thestarting winding ST and phasing capacitor C of the motor to start thesame. Because winding P2 is wound in opposite direction to winding Pl,theflux of winding P2 will cancel a portion of the flux of winding P1and thus cause a decrease of the voltage across secondary winding 8. Thenumber of turns of winding P2 is designed in such a way that when themotor is up to its normal speed, the flux of P2 will decrease the fluxof winding Pl so that the voltage induced in the secondary winding Swill not be sufficient to maintain conduction through switching deviceTRI. The starting winding of the motor will thus be disconnected.

Thermistor TH is connected across the secondary winding S to absorb thevoltage surges induced into the secondary winding due to sudden overloadcurrents flowing through the running winding of the motor M due tosudden changes in the load applied to the motor.

Because the thermistor TH has a predetermined fixed characteristic, itlimits the range of use of the starter device to a predetermined rangeof motor voltages, speeds and powers. In the embodiment of FIG. 2 therange of use of the starter device has been further extended byreplacing the thermistor TH of FIG. I by a potentiometer Pt forabsorbing the voltage surges induced in the secondary winding S and forpen'nitting adjustment of the voltage applied to the triac. The otherelement of the starter device of FIG. 2 are identical to the ones ofFIG. I and have been illustrated by the same reference characters. Byusing a potentiometer instead of a thermistor the opening of the triacbecomes adjustable at will for suiting various types of motors, thuswidening the range of use of the starter device in accordance with theinvention.

The advantage of the starter device of the invention is that it issubstantially independent of the nominal current and thus the horsepowerrating of the motor and that, consequently, it may be used with a widerange of motors. In fact, applicant has found that about three models ofstarters will be sufficient to start a group of motors ranging from 1/6to 1 HP. Indeed, the starter device of the invention is not responsiveto the difference between the starting and the running currents of themotor as it was the case for the devices of the prior art. On the l. Astarter device for a single phase A.C motor having a main winding and astarting winding adapted for connection to a single phase A.C. source,comprising a. a semi-conductor switching device having a controlelectrode and a transconductive path;

b. a transfonner having a first and a second primary windings arrangedto generate opposite fluxes in the transformer core, and a secondarywinding;

c. circuit means for connecting said first primary winding in serieswith the main winding of the motor;

d. circuit means for connecting said second primary winding in serieswith the transconductive path of the switching device and with thestarting of the motor; and

e. means for connecting the control electrode of said switching deviceto the secondary winding of said transformer, whereby the voltageinduced in said secondary winding by the initial inrush of currentthrough said first primary winding upon starting of the motor willrender said switching device conductive to permit energization of thestarting winding of the motor to start the motor, whereas the fluxproduced by said second primary winding shortly after initiation of theconduction of said switching device will oppose the flux created by saidprimary winding and so reduce the voltage induced in the secondarywinding to stop conduction through the switching device and thusdisconnect the starting winding of the motor.

2. A starter device as defined in claim 1, further comprising athermistor connected across said secondary winding for absorbing thevoltage surges induced in the secondary winding of the transformer dueto sudden overloads on the motor during operation causing correspondingincreases of the current through the first primary winding.

3. A starter device as defined in claim 1, wherein said switching deviceis a triac.

4. A starter device as defined in claim 1, wherein a potentiometer isconnected across said secondary winding, said potentiometer having avariable tap connected to said control electrode for varying the voltageapplied to said switching device and for absorbing the voltage surgesinduced in the

1. A starter device for a single phase A.C motor having a main windingand a starting winding adapted for connection to a single phase A.C.source, comprising : a. a semi-conductor switching device having acontrol electrode and a transconductive path; b. a transformer having afirst and a second primary windings arranged to generate opposite fluxesin the transformer core, and a secondary winding; c. circuit means forconnecting said first primary winding in series with the main winding ofthe motor; d. circuit means for connecting said second primary windingin series with the transconductive path of the switching device and withthe starting of the motor; and e. means for connecting the controlelectrode of said switching device to the secondary winding of saidtransformer, whereby the voltage induced in said secondary winding bythe initial inrush of current through said first primary winding uponstarting of the motor will render said switching device conductive topermit energization of the starting winding of the motor to start themotor, whereas the flux produced by said second primary winding shortlyafter initiation of the conduction of said switching deviCe will opposethe flux created by said primary winding and so reduce the voltageinduced in the secondary winding to stop conduction through theswitching device and thus disconnect the starting winding of the motor.2. A starter device as defined in claim 1, further comprising athermistor connected across said secondary winding for absorbing thevoltage surges induced in the secondary winding of the transformer dueto sudden overloads on the motor during operation causing correspondingincreases of the current through the first primary winding.
 3. A starterdevice as defined in claim 1, wherein said switching device is a triac.4. A starter device as defined in claim 1, wherein a potentiometer isconnected across said secondary winding, said potentiometer having avariable tap connected to said control electrode for varying the voltageapplied to said switching device and for absorbing the voltage surgesinduced in the secondary winding of the transformer due to suddenoverloads on the motor during operation causing corresponding increasesof the current through the first primary winding.